Abstract:

The present invention relates to a sheet, characterized in that two
opposite surfaces have elements which can transmit significant tensile
forces in the plane of the sheet.

Claims:

1.-14. (canceled)

15. A sheet which comprises two opposite surfaces which have elements
which can transmit significant tensile forces in the plane of the sheet.

16. The sheet according to claim 15, wherein the elements are hooks.

17. The sheet according to claim 15, wherein the elements are undercut
connections.

18. The sheet according to claim 15, wherein the elements are made of the
same material as the sheet.

19. The sheet according to claim 18, wherein the elements are part of the
sheet.

20. The sheet according to claim 19, wherein the elements are extruded
together with the sheet.

21. The sheet according to claim 15, wherein the sheet is made of
polycarbonate.

22. The sheet according to claim 15, wherein the sheet is a multi-wall
sheet.

23. The sheet according to claim 15, wherein the sheet is a solid sheet.

24. The sheet according to claim 15, wherein 2 pairs of opposite surfaces
have elements which can accommodate tensile forces in the plane of the
sheet.

25. The sheet according to claim 15, wherein the sheet has a span width of
more than 1.2 m.

26. The sheet according to claim 15, wherein the sheet has a span width of
more than 1.5 m.

27. The sheet according to claim 15, wherein the sheet has a span width of
more than 2.0 m.

28. The sheet according to claim 15, wherein the sheet has a span width of
more than 2.5 m.

29. A load-bearing system comprising the sheet according to claim 15 and a
connector profile.

30. An illumination system comprising the sheet according to claim 15
which is transparent to light and a connector profile.

Description:

[0001]The present invention relates to a sheet, characterized in that two
opposite surfaces have elements which can transmit significant tensile
forces in the plane of the sheet.

[0002]Sheets which carry loads under flexural stress are known from the
prior art. Such sheets carry loads, such as the intrinsic weight of the
sheet itself and surface loads, e.g. due to wind or snow, under flexural
stress and are regularly supported at the edges in a holding device
against forces acting perpendicularly to the sheet. If the load acting on
the sheet is too high, the sheet must be stabilized accordingly by
further supports, such as e.g. stays, so that it does not typically slip
from the support or kink in the middle of the span. The larger the sheet,
the more total load must be carried. As a result, a considerable number
of supports are as a rule required for larger constructions.

[0003]Sheets which have elements on two opposite surfaces which serve to
join adjacent sheets are also known from the prior art. Thus e.g. DE 31
26 440 describes sheets which serve as infill panels for stiffening
between two otherwise unstable profiles, i.e. in a similar manner to wind
bracings. DE-OS 2125725 describes sheets of plastic having elements where
only a joint connection is achieved, and the main load-bearing direction
runs in the direction of the joint (longitudinal direction). DE-OS 27 52
286 likewise describes sheets of plastic having elements with which only
a joint connection is achieved, and where no load initiation at the joint
into the sub-structure takes place. U.S. Pat. No. 4,573,300 also
described only sheets of plastic having elements where only a joint
connection is achieved, the main load-bearing direction is in the
longitudinal direction and where no load initiation at the joint into the
sub-structure takes place. The prior art described therefore comprises
only support widths in the transverse direction of the sheets of up to
approx. 1.20 m.

[0004]It has now been found that with the sheet according to the invention
higher span widths (support widths) can be achieved, since the sheet,
without hereby being restricted to the theory, can carry loads not
primarily under flexural stress, like a conventional sheet, but
predominantly under tensile stress.

[0005]In this context, sheet is to be understood as meaning a
substantially rectangular sheet of plastic. This can be a monolithic
sheet, also called a solid sheet, or a multi-shell sheet, also called a
multi-wall sheet. Such sheets are employed e.g. in wall or roof systems
where large load-bearing widths are to be spanned, e.g. modern
architecture, such as, for example, stadia. The technical requirements
and features of such sheets are described in European Technical Approval
Guideline 010 (STAG 010).

[0006]In a preferred embodiment, the invention relates to twin-wall sheets
or multi-wall sheets. Such sheets of polycarbonate, but also of other
plastics, are sufficiently known and are produced by means of extrusion.
They comprise the particular chords on the top and bottom, which are
spaced by a plurality of usually parallel bars at the particular
distance, in the present case in the region of 10 mm or more, and have
corresponding, often rectangular hollow spaces. Twin-wall sheets have a
top chord and a bottom chord and the bars lying in between. Multi-wall
sheets have, in addition to the top chord and a bottom chord and the
bars, further inner chords (intermediate chords) which usually run
parallel to the top chord and bottom chord. Triple-wall or four-wall
sheets etc. e.g. are referred to, according to the number of chords. In
addition to twin-wall sheets or multi-wall sheets with rectangular
geometries, there are also corresponding sheets with chords arranged at
an angle, which are e.g. also called framed sheets.

[0007]Twin-wall or multi-wall sheets according to the present invention
have a thickness of more than 4 mm, preferably 8 to 40, particularly
preferably 15 to 30 mm. The thickness here describes the distance between
the outer chords (top and bottom chord). Total thickness or sheet height
can also be referred to.

[0008]The present invention furthermore relates to such a sheet,
characterized in that it has a span width of more than 1.2 m, preferably
more than 1.5 m, very preferably more than 2.0 m and in particular more
than 2.5 m.

[0009]Conventional weights per unit area are in the region of more than
1.3 kg/m2, preferably 1.7 to 6, particularly preferably 2.5 to 5, in
particular 2.6 to 4 kg/m2.

[0010]Conventional thicknesses of the top and bottom chord are in the
range of from 0.5 to 4, particularly preferably 0.5 to 1.5 mm. The bars
and any intermediate chords present are as a rule significantly thinner,
e.g. 0.1 to 1.5 mm. Conventional sheet widths, which are determined by
the width of the extrusion die, are between 100 and 3,000 mm.
Conventional sheet lengths are in the range of from 500 mm to 15,000 mm.

[0011]Polycarbonate is sufficiently known as a thermoplastically
processable plastic. Polycarbonate plastics are predominantly aromatic
polycarbonates based on bisphenols, in particular bisphenol A.

[0012]The production of multi-wall sheets e.g. of polycarbonate is
sufficiently known and is described, for example, in "Technische
Thermoplaste, Kunststoff Handbuch 3/1, Hanser Verlag", Munich, in
particular pages 248-257.

[0013]The process for the application of additional layers, e.g. of
polycarbonate, to one or both surfaces of the top or bottom chord is
likewise sufficiently known (see e.g. EP-A 368 094, EP-A 372 213, EP-A 0
548 822). In this context, the covering layer can contain e.g. UV
absorbers or pearlescent pigments and can be applied by the route of
coextrusion or by lacquering or by reverse roll coating.

[0014]"Two opposite edges" here are to be understood as meaning two edges
which run parallel to one another or substantially parallel to one
another. More preferably, the edges are parallel, it being possible for
deviations of 5-10% to be tolerated.

[0015]In one embodiment, "elements" means specific shapings which serve
the purpose of fixing the sheet to tensile stress in a correspondingly
shaped support (positive tensile connection). Shaping here means that the
sheet itself is constructed such that the two opposite surfaces merge
into such shapings. For example, the sheet can have a depression, e.g. a
groove or a hook-like groove, parallel to these surfaces. A shaping in
the support which is substantially complementary in structure can then
engage accordingly into this groove. In another embodiment, the shaping
is an undercut connection.

[0016]In another embodiment, after its production the sheet is provided
with a device which serves the purpose of fixing the sheet to tensile
stress in a correspondingly shaped support. Such devices can be, for
example, tracks, which run along the opposite surfaces. Such devices can
in principle be made of any material which can accommodate the tensile
forces, such as e.g. metal or plastic. Known joining techniques can be
used to join the device to the sheet, such as e.g. gluing, welding,
riveting, screwing or clamping.

[0017]In one embodiment, the element is symmetric over the length of the
sheet, i.e. is uniformly configured along the top opposite surfaces along
the entire length. In a further embodiment, the element is configured
along 50%, preferably along 90% of the length of the surface. In a
further embodiment, the elements are symmetrical on both sides.

[0018]"Have" here means that the said opposite surfaces and the elements
can be connected to one another in any desired form; the elements can be
part of the sheet and therefore of the surface, e.g. in the case of an
extruded sheet can have been extruded together with this, or the elements
can also have been applied subsequently, thus e.g. such as a track or
strip of the material of the sheet or of another material.

[0019]In the present connection, the feature "can transmit significant
tensile forces in the plane of the sheet" means that the elements can
transmit tensile forces between the sheet and a suitable holding device
which holds the element. Tensile forces are regarded as significant here
if a significant portion of the intrinsic weight of the sheet itself and
surface loads, e.g. due to wind or snow, can thereby be carried, in
particular more than 60%, preferably more than 70%, particularly
preferably more than 80%, in particular more than 90%. The sheet can thus
to a certain extent be tensioned like a membrane between the two opposite
surfaces, or can become tensioned itself under load (similarly to a cable
construction). In one embodiment, the fixing device is configured such
that material stresses of 20 MPa are not exceeded.

[0020]It is to be pointed out that in multi-wall sheets from the prior
art, the main load-bearing direction is in the longitudinal direction,
and only an insignificantly portion is carried in the transverse
direction, while in the sheets according to the invention the main
load-bearing direction is in the transverse direction.

[0021]The surface loads are removed into the support. It has been found
that the sheets according to the invention cannot slip from the support,
since they are anchored, and that no kinking of the sheet occurs in the
middle of the span, since scarcely any flexural stress takes place in the
middle of the span.

[0022]In one embodiment, the sheet is transparent to light. The term
"transparent to light" relates to the visible spectral range; the
wavelength range of from 380 to 780 nm, in particular the wavelength of
550 nm serves for the characterization. The light transparency, which is
designated T here, is predominantly symbolized by τD65 in the
scientific literature. The base material and the binder should have a
light transparency T of at least 50%, preferably 60 to 94%.

[0023]Known thermoplastics are suitable for production of the sheet. For
example, polycarbonate, polystyrene, polymethyl methacrylate,
polyethylene, polypropylene, polyvinyl chloride, polyester,
acrylo-butadiene-styrene and blends therefore can be used. These are
described in Saechtling, "Kunststoff Taschenbuch" 28th ed. (2001),
chapter 4, Hanser Verlag, Munich, Vienna

[0024]The present sheet is therefore particularly suitable for the
production of load-bearing systems which can be employed as roof or wall
systems, in particular as illumination systems. The present invention
therefore also provides a connector profile which can accommodate the
shaping of the sheet. Such a connector profile is preferably constructed
as a two-part track, the lower part of which is laid on a suitable
support. The sheet is then laid on this lower part, and the upper part of
the connector profile is fixed to the lower part, in order to fix the
sheet in between.

[0025]In one embodiment, the invention therefore also relates to an
illumination system comprising a sheet according to the invention which
is transparent to light and a connector profile.